The present invention relates to a method producing a high strength and hard metallic composite layer material which is composed of several metal layers connected with one another by diffusion welding.
Metallic composite layer materials are composed of two or more metal layers which are connected with one another and identified as components. The components predominant in volume or weight are identified as base or backing material, while the remaining components depending on their position and arrangement are identified as plating, supporting, inserting or intermediate material.
The combination of suitable metals and alloys in connection with the selection of suitable layer thicknesses and the relative position of the components in a composite provides for a possibility of producing of almost unlimited number of composite layer materials with defined physical, chemical and technological properties.
Typical examples of composite layer materials are unalloyed and low alloyed steel which for the corrosion protection are "plated" with protective layers of corrosion and heat resistant steels, non-ferrous metals and noble metals which at high chemical, mechanical and thermal stresses are used as correspondingly strongly dimensioned structural elements of steel, non-ferrous metals or noble metals in an efficient way.
The inexpensive base material of unalloyed or low alloyed steel takes up the mechanical loading, while the chemical/thermal loading is taken by the plating material.
The metallic composite layer materials are mainly produced by processes in which the individual metal layers are connected in a solid phase with one another under increased temperature by pressure, and each layer component maintains its original properties. Such processes include pressure welding, roller plating and explosion plating. More recently the hot isostatic pressing (HIP-process) is used for producing of metallic composite layer materials especially for complicated shaped structural elements. During this process the metal components are surrounded by a gas-tight deformable sleeve, and at temperatures selected so high that a sufficient diffusion of the components in one another can occur, are connected with one another by gases acting through the outer wall of the sleeve under pressure, by diffusion welding.
The strength value tensile strength, yielding point) of a structural element of metallic composite layer materials is obtained additively from the respective values of the individual layer components. When a metallic composite layer material, for example of several steel layers of high strength (greater than 1,500 and up to 2,500 N/mm pulling strength) is produced, the individual steel layers have this value before the diffusion welding.
There is a great number of "highest strength" steels which possess such a strength due to their alloy content of strength-increasing elements, such as chromium, nickel, cobalt, molybdenum or also nitrogen in raw condition. These steels are however difficult to deform, especially by rolling to thin sizes, such as sheets or bands, for use as layer components. They have a high form change resistance which under the action of high deformation degrees increases further and therefore significantly reduces the possibilities of deformation. Special precautionary measures must be taken during rolling of such steels, for example rolling in several heating stages with maintaining very narrow limited deformation temperatures, to roll such high strength steels to thin sizes. These processes of producing layer components made of steel, are not economical.
A further possibility to use high strength layer components made of steel for forming a composite layer material is to roll steels with a basic composition insuring a good workability to flat products, and then to raise their strength either by a combined hardening tempering treatment producing a martensite structure or by a precipitation hardening treatment by which intermetallic compounds, like carbides nitrides, etc precipitate and harden the steel.
The thusly expanded strength properties were again restored during subsequent connection of the thusly treated steel layer components to a composite body at high temperatures up to 1,300.degree. C. required for diffusion welding.